The subject invention is directed toward the art of angiographic catheters and to catheter manufacturing methods and, more particularly, to a catheter having an improved unitary construction and to an improved method for manufacturing multiples of such catheters from a continuous feedstock.
Angiographic catheters are used for diagnostic purposes as well as for angioplasty. It is generally agreed that a good catheter should have the following features:
a) torsion control with a 1:1 rotation about its central longitudinal axis even when subjected to curvatures of as much as 110.degree. along the catheter's length; PA1 b) the ability to withstand high injection pressures of as much as 1000 PSI which are required where large amounts of contrast media is needed to properly visualize a given area to be studied; PA1 c) push ability in conjunction with good torsional control along its axis mandates a catheter body having a controlled rigidity since if too rigid, it can cause injury and if too flexible, it may buckle; PA1 d) a controlled degree of flexibility at the catheter tip is necessary to prevent injury to vessel openings and to vessel walls and this can be accomplished by using a softer plastic in this region, annular grooving, or decreasing the diameter as compared to the catheter body; and, PA1 e) the catheter tip must be easily formed and must retain the formed shape even when subjected to straightening when passed over a guide wire. PA1 1) The process starts by forming a length of elastomeric tube. The tube is formed by starting with a silver plated copper wire or a monofilament of plastic (such as "Celcon" manufactured by the Hoechst Celanese Corporation, or Ultraform, an acetal copolymer manufactured by BASF), of a diameter equal to the published lumen diameter of the catheter being manufactured. This wire or monofilament is referred to as the "mandrel." As an example, a standard French 7 catheter has a lumen of 0.046 inches and an outside diameter of 0.092 inch. The wire or monofilament is purchased and used in continuous lengths of over 5000 feet. This wire or monofilament is referred to as a "mandrel" because the catheter is built on it. PA1 2) The coated mandrel is then placed in a "braiding machine" which overlays the elastomeric tube extrusion with multiple (e.g., 16) strands of 0.003 inch or smaller diameter stainless steel wire. PA1 3) After the entire length of elastomeric extrusion has been overlaid with the wire braid, it is then cleaned in an ultrasonic cleaning bath and again passed through the plastic extruder adding another layer of plastic creating a wall thickness of approximately 0.012 inch. The combined layers of plastic and wire braid on the 0.046 inch diameter mandrel will now be approximately 0.094 inch in diameter. PA1 4) Catheter tip material requires only a single extrusion on a corresponding mandrel wire because no braiding is required. The single layer of plastic applied to a 0.046 inch mandrel will have a wall thickness of 0.024 inch for a total diameter of 0.094 inch. PA1 5) The body material and the tip material is cut to lengths of approximately 42 inches. This mandrel is now removed from within the cut lengths of body and tip material. This is done by stretching the mandrel, if necessary, to reduce its diameter and facilitate its withdrawal from within the plastic extrusion. PA1 6) This material is then passed through a centerless grinder and ground to the proper diameter size and to a fine, smooth surface. PA1 7) The tip material is then cut to lengths of approximately 31/2 inches and tapers are ground on one end where necessary and a flare is formed at the other end. PA1 8) The body material is ground to a taper at one end to mate with the internal taper of the flared tip portion. PA1 9) A steel rod approximately 0.044 inch diameter is inserted into a catheter body and a tip is slipped onto the rod and the external taper of the body is mated with the internal taper of the tip. PA1 10) Next, a sleeve or tube of Teflon about 6 inches in length is passed over the tip-body mated section. The tip-body with the Teflon sleeve are then pressed through a die that has been heated to approximately 325.degree. F. The heat plus the pressure of the sleeve fuses and mold the joined sections by melting the plastic of both parts into a smooth joint. Where necessary, the catheter assembly is again passed through the centerless grinder, particularly if the fused joint is slightly larger than the rest of the catheter. It is important that the catheter with tip be within + or -0.001 inch of the published diameter. PA1 11) The finished catheter is cut to the published length, a luer hub is added to the proximal end and the tip portion is then shaped with a forming wire in boiling water. The shapes of catheter tips are many, such as a single curve, double curve, Judkins left, Judkins right, pigtail, etc.
A catheter with the above features is described in my prior U.S. Pat. No. 3,485,234, which issued Dec. 23, 1969. My prior U.S. Pat. No. 3,585,707, which issued Jun. 22, 1971, sets forth how to make or manufacture the catheter.
The catheter construction described in these prior patents uses a wire braid reinforcing to provide torsional control and to strengthen the catheter body to better withstand high pressure injections. In order to have a flexible tip with good shape memory, it is necessary that no wire braid be in the tip area. The earlier patents describe the manner in which a tip portion is added to the catheter body. The tip portion, without braid, is formed as a separate item and is molded or fused to the end of the catheter body. This has been the weakest portion of the catheter, since the tip may become loosened or separated over a period of time or from physical abuse such as using an oversized guide wire, severe twisting or attempts at re-shaping the curvature of the tip.
The original manufacturing process used for making the original older catheters of the type described above is generally set forth in the flow chart of FIG. 1. In particular, the process involves the following steps (the paragraph numbers correspond to the sequence numbers shown in FIG. 1):
The mandrel is passed through a plastic extruder, coating the mandrel with the selected elastomer to approximately 0.006 inch wall thickness. The elastomer or plastic used, for example, could be polyurethane containing bismuth or barium to make it opaque to x-rays, or radiopaque.
One major problem with the original construction of these earlier catheters is that it has been necessary to mold or fuse the tip by hand. This is very labor intensive and, therefore, expensive. In an age of rising medical costs, it is even more important than ever to reduce manufacturing costs.
My earlier related co-pending application teaches a novel catheter construction and a method which eliminates the need to manually mold or fuse the tip to thereby allow the catheter to be made as a single, unitary construction. All of the good features of the original catheter construction have been preserved in the method and apparatus of my earlier application including the wire braid in the body of the catheter and the absence or lack of wire braid in the tip area. The method of my earlier application is fully automated, eliminating the hand crafting of the catheter tip. This makes the catheter taught there safer and less expensive to manufacture than the original early styles.
In accordance with my earlier co-pending application and with reference now to FIGS. 2a-2f, the method of manufacturing angiographic catheters, each having an overall length L, generally comprises forming a length of cylindrical elastomeric tube 10 of a predetermined outer diameter (FIG. 2a) and braiding multiple strands of fine stainless steel wire wrapping about the elastomeric tube, forming a braided tube construction 12 shown in FIG. 2b. Thereafter, a bonding agent or adhesive is applied to the braided construction circumferentially thereof at spaced locations 14, 16 and 18 as showl in FIG. 2c causing the strands of wire wrapping to be bonded to each other and to the elastomer. Subsequent to the bonding, predetermined sections of the wire wrapping are removed from the elastomeric tube to leave a length of elastomeric tube with multiple wire wrapped sections 20, 22, 24 and 26 spaced from one another by unwrapped sections 30, 32 and 34 such that each wire wrapped section 20, 22, 24 and 26 has axially spaced ends enclosed by the bonding agent (e.g., wire wrapped section 22 has axial spaced ends at the unwrapped sections 30, 32) to prevent loosening or unwinding of the wire wrapping as best shown in FIG. 2d. A continuous layer of an elastomer is coated over the length of the elastomeric tube with multiple wire-wrapped sections to produce a uniform diameter length 36 of elastomeric coated wire-wrapped sections spaced apart from one another by unwrapped sections as shown in FIG. 2e. The continuous length thus produced is thereafter cut transversely at locations selected to reduce the length to multiple pieces of coated wire-wrapped sections having length L, each having a coated, unwrapped section joined thereto on at least one end thereof forming a catheter 38 having a preferred unitary construction as shown in FIG. 2f.
The manufacturing method described in my earlier filed co-pending application and briefly here is substantially more efficient than the original prior art methods described above in this specification and produces catheters having superior characteristics over the original prior art devices. However, the steps required to apply the bonding agent or adhesive at the various spaced-apart locations have proven to be somewhat of a time constraint in the manufacturing process. In that regard, the adhesive requires a cure time before the grinding process can begin. Even through the use of heat or UV curing, the drying cycle takes a finite amount of time. Also, the starting and stopping of the longitudinal motion of the mandrel first at each elastomeric layer site and then at each grinding section site spaced apart by a length L is somewhat time consuming and produces undesirable wear and tear on the catheter manufacturing apparatus.
It would therefore be desirable to manufacture multiple catheters from a single feedstock using a continuous process of depositing a uniform layer of a bonding agent directly onto the wire braiding. In order to reduce manufacturing cycle time, it would be desirable to deposit the bonding agent onto the entire length of feedstock covered with the wire braiding in a single manufacturing operation. It would further be desirable to deposit the bonding agent directly onto the wire braiding using an extrusion process.